cmd/compile: compute second method type at runtime

The type information for a method includes two variants: a func
without the receiver, and a func with the receiver as the first
parameter. The former is used as part of the dynamic interface
checks, but the latter is only returned as a type in the
reflect.Method struct.

Instead of computing it at compile time, construct it at run time
with reflect.FuncOf.

Using cl/20701 as a baseline,

	cmd/go: -480KB, (4.4%)
	jujud:  -5.6MB, (7.8%)

For #6853.

Change-Id: I1b8c73f3ab894735f53d00cb9c0b506d84d54e92
Reviewed-on: https://go-review.googlesource.com/20709
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -505,7 +505,6 @@ func dextratypeData(s *Sym, ot int, t *Type) int {
 
 		ot = dgopkgpath(s, ot, a.pkg)
 		ot = dmethodptr(s, ot, dtypesym(a.mtype))
-		ot = dmethodptr(s, ot, dtypesym(a.type_))
 		ot = dmethodptr(s, ot, a.isym)
 		ot = dmethodptr(s, ot, a.tsym)
 	}

src/cmd/link/internal/ld/deadcode.go

@@ -95,7 +95,7 @@ func deadcode(ctxt *Link) {
 				// and setting those fields to nil. Doing so
 				// would reduce the binary size of typical
 				// programs like cmd/go by ~2%.
-				d.markMethodType(m)
+				d.mark(m.mtyp(), m.src)
 				rem = append(rem, m)
 			} else {
 				rem = append(rem, m)
@@ -171,18 +171,17 @@ var markextra = []string{
 }
 
 // methodref holds the relocations from a receiver type symbol to its
-// method. There are four relocations, one for each of the fields in
-// the reflect.method struct: mtyp, typ, ifn, and tfn.
+// method. There are three relocations, one for each of the fields in
+// the reflect.method struct: mtyp, ifn, and tfn.
 type methodref struct {
 	m   methodsig
 	src *LSym     // receiver type symbol
-	r   [4]*Reloc // R_METHOD relocations to fields of runtime.method
+	r   [3]*Reloc // R_METHOD relocations to fields of runtime.method
 }
 
 func (m methodref) mtyp() *LSym { return m.r[0].Sym }
-func (m methodref) typ() *LSym  { return m.r[1].Sym }
-func (m methodref) ifn() *LSym  { return m.r[2].Sym }
-func (m methodref) tfn() *LSym  { return m.r[3].Sym }
+func (m methodref) ifn() *LSym  { return m.r[1].Sym }
+func (m methodref) tfn() *LSym  { return m.r[2].Sym }
 
 func (m methodref) isExported() bool {
 	for _, r := range m.m {
@@ -233,12 +232,6 @@ func (d *deadcodepass) markMethod(m methodref) {
 	}
 }
 
-// markMethodType marks just a method's types as reachable.
-func (d *deadcodepass) markMethodType(m methodref) {
-	d.mark(m.mtyp(), m.src)
-	d.mark(m.typ(), m.src)
-}
-
 // init marks all initial symbols as reachable.
 // In a typical binary, this is INITENTRY.
 func (d *deadcodepass) init() {

src/cmd/link/internal/ld/decodesym.go

@@ -351,6 +351,6 @@ func decodetype_methods(s *LSym) []methodsig {
 		panic(fmt.Sprintf("method slice pointer in %q leads to a different symbol", s.Name))
 	}
 	off = int(r.Add)                    // array of reflect.method values
-	sizeofMethod := 6 * Thearch.Ptrsize
+	sizeofMethod := 5 * Thearch.Ptrsize // sizeof reflect.method in program
 	return decode_methodsig(s, off, sizeofMethod, numMethods)
 }

src/reflect/type.go

@@ -291,7 +291,6 @@ type method struct {
 	name    *string        // name of method
 	pkgPath *string        // nil for exported Names; otherwise import path
 	mtyp    *rtype         // method type (without receiver)
-	typ     *rtype         // .(*FuncType) underneath (with receiver)
 	ifn     unsafe.Pointer // fn used in interface call (one-word receiver)
 	tfn     unsafe.Pointer // fn used for normal method call
 }
@@ -561,11 +560,29 @@ func (t *rtype) pointers() bool { return t.kind&kindNoPointers == 0 }
 
 func (t *rtype) common() *rtype { return t }
 
-func (t *uncommonType) Method(i int) (m Method) {
-	if t == nil || i < 0 || i >= len(t.methods) {
+func (t *rtype) NumMethod() int {
+	if t.Kind() == Interface {
+		tt := (*interfaceType)(unsafe.Pointer(t))
+		return tt.NumMethod()
+	}
+	ut := t.uncommon()
+	if ut == nil {
+		return 0
+	}
+	return len(ut.methods)
+}
+
+func (t *rtype) Method(i int) (m Method) {
+	if t.Kind() == Interface {
+		tt := (*interfaceType)(unsafe.Pointer(t))
+		return tt.Method(i)
+	}
+	ut := t.uncommon()
+
+	if ut == nil || i < 0 || i >= len(ut.methods) {
 		panic("reflect: Method index out of range")
 	}
-	p := &t.methods[i]
+	p := &ut.methods[i]
 	if p.name != nil {
 		m.Name = *p.name
 	}
@@ -574,60 +591,41 @@ func (t *uncommonType) Method(i int) (m Method) {
 		m.PkgPath = *p.pkgPath
 		fl |= flagStickyRO
 	}
-	mt := p.typ
+	ft := (*funcType)(unsafe.Pointer(p.mtyp))
+	in := make([]Type, 0, 1+len(ft.in()))
+	in = append(in, t)
+	for _, arg := range ft.in() {
+		in = append(in, arg)
+	}
+	out := make([]Type, 0, len(ft.out()))
+	for _, ret := range ft.out() {
+		out = append(out, ret)
+	}
+	mt := FuncOf(in, out, p.mtyp.IsVariadic())
 	m.Type = mt
 	fn := unsafe.Pointer(&p.tfn)
-	m.Func = Value{mt, fn, fl}
+	m.Func = Value{mt.(*rtype), fn, fl}
 	m.Index = i
-	return
+	return m
 }
 
-func (t *uncommonType) NumMethod() int {
-	if t == nil {
-		return 0
+func (t *rtype) MethodByName(name string) (m Method, ok bool) {
+	if t.Kind() == Interface {
+		tt := (*interfaceType)(unsafe.Pointer(t))
+		return tt.MethodByName(name)
 	}
-	return len(t.methods)
-}
-
-func (t *uncommonType) MethodByName(name string) (m Method, ok bool) {
-	if t == nil {
-		return
+	ut := t.uncommon()
+	if ut == nil {
+		return Method{}, false
 	}
 	var p *method
-	for i := range t.methods {
-		p = &t.methods[i]
+	for i := range ut.methods {
+		p = &ut.methods[i]
 		if p.name != nil && *p.name == name {
 			return t.Method(i), true
 		}
 	}
-	return
-}
-
-// TODO(rsc): gc supplies these, but they are not
-// as efficient as they could be: they have commonType
-// as the receiver instead of *rtype.
-func (t *rtype) NumMethod() int {
-	if t.Kind() == Interface {
-		tt := (*interfaceType)(unsafe.Pointer(t))
-		return tt.NumMethod()
-	}
-	return t.uncommon().NumMethod()
-}
-
-func (t *rtype) Method(i int) (m Method) {
-	if t.Kind() == Interface {
-		tt := (*interfaceType)(unsafe.Pointer(t))
-		return tt.Method(i)
-	}
-	return t.uncommon().Method(i)
-}
-
-func (t *rtype) MethodByName(name string) (m Method, ok bool) {
-	if t.Kind() == Interface {
-		tt := (*interfaceType)(unsafe.Pointer(t))
-		return tt.MethodByName(name)
-	}
-	return t.uncommon().MethodByName(name)
+	return Method{}, false
 }
 
 func (t *rtype) PkgPath() string {

src/runtime/type.go

@@ -155,7 +155,6 @@ type method struct {
 	name    *string
 	pkgpath *string
 	mtyp    *_type
-	typ     *_type
 	ifn     unsafe.Pointer
 	tfn     unsafe.Pointer
 }